The present invention generally relates to electrochemical cells (i.e., batteries) and, more particularly, relates to a low volume collector assembly for collecting electrical current and sealing closed the open end of an electrochemical cell container.
Conventional alkaline electrochemical cells generally include a cell container in the form of a cylindrical steel can having a closed bottom end, a cylindrical side wall and an open top end. Disposed within the steel can is a positive electrode, also referred to as the cathode, and a negative electrode, also referred to as the anode. The cathode typically employs manganese dioxide as the active material, while the negative electrode typically employs zinc powder as the active material. In bobbin-type cells, the cathode is typically formed in a tubular shape with the outer surface engaging the interior surface of the steel can, and the anode is generally formed in the shape of a cylinder centrally disposed in the can. A separator is located between the anode and the cathode, and an alkaline electrolyte solution simultaneous contacts the anode, the cathode and the separator.
The steel can is typically in electrical contact with a positive contact terminal at the closed end and the outer surface of the cathode, and thus serves as the cathode current collector. An anode current collector is typically inserted into the anode to provide an electrical path for current to pass to a negative outer terminal provided at the open end of the can. The anode current collector is typically assembled as a component of a collector assembly that provides closure to the open end of the steel can to seal the active electrochemical materials in a sealed volume of the can. The collector assembly typically employs an annular polymeric (e.g., nylon) seal, the negative outer terminal, and the current collector, and may further include an inner neutral cover that radially supports the seal. In some cells the collector assembly further includes a Belleville washer and spur.
Conventional cylindrical alkaline cells are typically sealed closed by placing the collector assembly in the open end of the steel can and crimping the open end of the can inwardly and over the outer periphery of the collector assembly to compress the seal. The conventional electrochemical cell employs an electrically conductive current collector, typically in the shape of an elongated brass nail, inserted into the anode active material. The current collector nail generally extends through a central opening provided in the hub of the seal and provides an electrical connection between the anode and the outer conductive cover which serves as the battery cell negative terminal. The elongated brass nail generally extends into the anode by a considerable length (e.g., 80%) and has a sufficiently large diameter such that the nail consumes considerable volume within the can. The current collector is typically welded or otherwise press fit to the negative terminal to maintain suitable electrical contact therebetween.
The conventional collector assembly typically made up of the brass nail, annular nylon seal, outer negative cover and an inner neutral cover requires many components. The components making up the collector assembly add to the overall component cost, and require costly equipment to manufacture and assemble. Additionally, the conventional elongated current collector nail and other components of the collector assembly typically consume a substantial useable volume within the cell, which limits the amount of volume available for electrochemically active materials. Further, the conventional elongated nail collector design usually requires a welding or press fit connection between the outer terminal which involves additional equipment costs and process steps and, with the press fit assembly, may result in electrical contact problems and reduced reliability.
Accordingly, there exists a need for a cost affordable and improved current collector assembly that may be easily assembled into an electrochemical cell. There further exists a need for an electrochemical cell that employs a current collector assembly that consumes less volume within the can, thereby leaving more useable volume for electrochemically active materials.